Fraud-based tax determination: notice triggers interest and scaled penalty provisions allowing payment to conclude proceedings. Where tax is unpaid, short paid, erroneously refunded, or input tax credit wrongly availed by reason of fraud, wilful misstatement or suppression, the proper officer shall serve a show-cause notice specifying tax, interest and a penalty equivalent to the tax; related statements may be treated as notices where grounds (other than fraud) are the same, and the officer, after considering representations, shall determine and order tax, interest and penalty within five years from the annual return due date or erroneous refund.